fetch() global function
Baseline Widely available
This feature is well established and works across many devices and browser versions. It’s been available across browsers since March 2017.
Note: This feature is available in Web Workers.
The global fetch()
method starts the process of fetching a resource from the network, returning a promise that is fulfilled once the response is available.
The promise resolves to the Response
object representing the response to your request.
A fetch()
promise only rejects when the request fails, for example, because of a badly-formed request URL or a network error.
A fetch()
promise does not reject if the server responds with HTTP status codes that indicate errors (404
, 504
, etc.).
Instead, a then()
handler must check the Response.ok
and/or Response.status
properties.
The fetch()
method is controlled by the connect-src
directive of Content Security Policy rather than the directive of the resources it's retrieving.
Note: The fetch()
method's parameters are identical to those of the Request()
constructor.
Syntax
fetch(resource)
fetch(resource, options)
Parameters
resource
-
This defines the resource that you wish to fetch. This can either be:
- A string or any other object with a stringifier — including a
URL
object — that provides the URL of the resource you want to fetch. - A
Request
object.
- A string or any other object with a stringifier — including a
options
Optional-
An object containing any custom settings you want to apply to the request. The possible options are:
body
-
Any body that you want to add to your request: this can be a
Blob
, anArrayBuffer
, aTypedArray
, aDataView
, aFormData
, aURLSearchParams
, string object or literal, or aReadableStream
object. This latest possibility is still experimental; check the compatibility information to verify you can use it. Note that a request using theGET
orHEAD
method cannot have a body. browsingTopics
Experimental-
A boolean specifying that the selected topics for the current user should be sent in a
Sec-Browsing-Topics
header with the associated request. See Using the Topics API for more details. cache
-
A string indicating how the request will interact with the browser's HTTP cache. The possible values,
default
,no-store
,reload
,no-cache
,force-cache
, andonly-if-cached
, are documented in the article for thecache
property of theRequest
object. credentials
-
Controls what browsers do with credentials (cookies, HTTP authentication entries, and TLS client certificates). Must be one of the following strings:
omit
: Tells browsers to exclude credentials from the request, and ignore any credentials sent back in the response (e.g., anySet-Cookie
header).same-origin
: Tells browsers to include credentials with requests to same-origin URLs, and use any credentials sent back in responses from same-origin URLs. This is the default value.include
: Tells browsers to include credentials in both same- and cross-origin requests, and always use any credentials sent back in responses.Note: Credentials may be included in simple and "final" cross-origin requests, but should not be included in CORS preflight requests.
headers
-
Any headers you want to add to your request, contained within a
Headers
object or an object literal withString
values. Note that some names are forbidden.Note: The
Authorization
HTTP header may be added to a request, but will be removed if the request is redirected cross-origin. integrity
-
Contains the subresource integrity value of the request (e.g.,
sha256-BpfBw7ivV8q2jLiT13fxDYAe2tJllusRSZ273h2nFSE=
). keepalive
-
The
keepalive
option can be used to allow the request to outlive the page. Fetch with thekeepalive
flag is a replacement for theNavigator.sendBeacon()
API. method
-
The request method, e.g.,
"GET"
,"POST"
. The default is"GET"
. Note that theOrigin
header is not set on Fetch requests with a method ofHEAD
orGET
. (This behavior was corrected in Firefox 65 — see Firefox bug 1508661.) Any string which is a case-insensitive match for one of the methods in RFC 9110 will be uppercased automatically. If you want to use a custom method (likePATCH
), you should uppercase it yourself. mode
-
The mode you want to use for the request, e.g.,
cors
,no-cors
, orsame-origin
. priority
-
Specifies the priority of the fetch request relative to other requests of the same type. Must be one of the following strings:
redirect
-
How to handle a
redirect
response:follow
-
Automatically follow redirects. Unless otherwise stated the redirect mode is set to
follow
. error
-
Abort with an error if a redirect occurs.
manual
-
Caller intends to process the response in another context. See WHATWG fetch standard for more information.
referrer
-
A string specifying the referrer of the request. This can be a same-origin URL,
about:client
, or an empty string. referrerPolicy
-
Specifies the referrer policy to use for the request. May be one of
no-referrer
,no-referrer-when-downgrade
,same-origin
,origin
,strict-origin
,origin-when-cross-origin
,strict-origin-when-cross-origin
, orunsafe-url
. signal
-
An
AbortSignal
object instance; allows you to communicate with a fetch request and abort it if desired via anAbortController
.
Return value
Exceptions
AbortError
DOMException
-
The request was aborted due to a call to the
AbortController
abort()
method. NotAllowedError
DOMException
-
Usage of the Topics API is specifically disallowed by a
browsing-topics
Permissions Policy, and afetch()
request was made withbrowsingTopics: true
. TypeError
-
Can occur for the following reasons:
Reason | Failing examples |
---|---|
Invalid header name. |
// space in "C ontent-Type" const headers = { 'C ontent-Type': 'text/xml', 'Breaking-Bad': '<3', }; fetch('https://example.com/', { headers }); |
Invalid header value. The header object must contain exactly two elements. |
const headers = [ ['Content-Type', 'text/html', 'extra'], ['Accept'], ]; fetch('https://example.com/', { headers }); |
Invalid URL or scheme, or using a scheme that fetch does not support, or using a scheme that is not supported for a particular request mode. |
fetch('blob://example.com/', { mode: 'cors' }); |
URL includes credentials. |
fetch('https://user:password@example.com/'); |
Invalid referrer URL. |
fetch('https://example.com/', { referrer: './abc\u0000df' }); |
Invalid modes (navigate and websocket ). |
fetch('https://example.com/', { mode: 'navigate' }); |
If the request cache mode is "only-if-cached" and the request mode is other than "same-origin". |
fetch('https://example.com/', { cache: 'only-if-cached', mode: 'no-cors', }); |
If the request method is an invalid name token or one of the forbidden headers
('CONNECT' , 'TRACE' or 'TRACK' ).
|
fetch('https://example.com/', { method: 'CONNECT' }); |
If the request mode is "no-cors" and the request method is not a CORS-safe-listed method
('GET' , 'HEAD' , or 'POST' ).
|
fetch('https://example.com/', { method: 'CONNECT', mode: 'no-cors', }); |
If the request method is 'GET' or 'HEAD' and the body is non-null or not undefined. |
fetch('https://example.com/', { method: 'GET', body: new FormData(), }); |
If fetch throws a network error. |
Examples
In our Fetch Request example (see Fetch Request live) we
create a new Request
object using the relevant constructor, then fetch it
using a fetch()
call. Since we are fetching an image, we run
Response.blob()
on the response to give it the proper MIME type so it will be
handled properly, then create an Object URL of it and display it in an
<img>
element.
const myImage = document.querySelector("img");
const myRequest = new Request("flowers.jpg");
fetch(myRequest)
.then((response) => {
if (!response.ok) {
throw new Error(`HTTP error! Status: ${response.status}`);
}
return response.blob();
})
.then((response) => {
myImage.src = URL.createObjectURL(response);
});
In our Fetch Request with init example (see Fetch Request init live) we do the same thing except that we pass in an options object when we invoke fetch()
.
In this case, we can set a Cache-Control
value to indicate what kind of cached responses we're okay with:
const myImage = document.querySelector("img");
const reqHeaders = new Headers();
// A cached response is okay unless it's more than a week old
reqHeaders.set("Cache-Control", "max-age=604800");
const options = {
headers: reqHeaders,
};
// Pass init as an "options" object with our headers.
const req = new Request("flowers.jpg", options);
fetch(req).then((response) => {
// ...
});
You could also pass the init
object in with the Request
constructor to get the same effect:
const req = new Request("flowers.jpg", options);
You can also use an object literal as headers
in init
:
const options = {
headers: {
"Cache-Control": "max-age=60480",
},
};
const req = new Request("flowers.jpg", options);
Specifications
Specification |
---|
Fetch Standard # fetch-method |
Browser compatibility
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